Despite a wide array of fundamental data concerning the dorsal cochlear nucleus and despite the prevalence of acoustic gliomas and meningiomas involving it, little or nothing is yet known either about its contribution to hearing or the deficits in hearing that accompany its damage as a result of injury or disease. This project includes a series of tissue-level ablation-behavior experiments on the dorsal cochlear nucleus of the cat. Cats with and without ablation of the dorsal cochlear nucleus will be tested on a variety of auditory psychophysical tasks. The psychophysical tests themselves are derived from the cytoarchitecture, the intrinsic and extrinsic afferent and efferent connections, and the electrophysiological and neurochemical characteristics of the dorsal cochlear nucleus and its constituent neural elements. Because the dorsal cochlear nucleus takes on somewhat different forms in different orders of mammals and these differences form the basis of some of the behavioral tests included, a complete inquiry must eventually make use of several carefully selected species of mammals. However, only cats will be used in the present series of exploratory experiments because of the vastly greater body of knowledge that is already available on their auditory system.